1. introduction to stars
DESCRIPTION
cmgTRANSCRIPT
Builder Slide FormatSupport different gridding systems
Used as chemical simulators
*
*
CMG Simulation Technology
A mathematical model accounting for the propagation of (true, pseudo, and/or dispersed phase) components through a porous medium and their effects on fluid and rock properties
Can be employed as a multi-component, multi-phase isothermal reservoir simulator
(Full material / mass balance equations)
*
CMG Simulation Technology
A mathematical model accounting for the propagation of heat through a porous medium and its effect on fluid and rock properties
(Full energy balance equation)
Stable implicit formulation
*
*
Water
Water is a standard component, and internal defaults are available for
Density, viscosity, enthalpy, heat capacity
Polymer solution
*
Internal water K values
Salt, ion component
*
Pure components
Chemicals of interest, soluble in oil (CO2, H2S, naptha, etc.)
Gas components, when soluble in oil (N2, O2, etc.)
*
e.g. methane, propane, hexane, oxygen, CO2, decane, etc.
*
Oil component in black-oil model
Pairs or limited groups (C7 - C9)
Entire ranges of molecular weight (Mw = 200 to 400)
Distribution of molecular species is fixed
*
Choice of oil components
For EOR processes, the choice of oil components is usually determined entirely by the type of mechanisms important to the EOR process to be modeled, for example:
Vaporization
A single component with zero K value (dead oil) allows for no vaporization or distillation
Single component with non zero K value allows for vaporization, but no distillation
Need at least two components for distillation (oil and solution gas in black-oil model)
*
Reactions are between oil components
Reaction models and strategy may determine what oil components to use
Cracking fuel from asphaltene
e.g. Hydrocarbon + Oxygen CO2 + H20 + Energy
*
CMG Simulation Technology
Temperature dependence of many properties can be estimated by running the EOS package at various temperatures (WinProp)
An oil can be characterized accurately from PVT and VLE lab data with many components (10 - 20), and then the result of lumping to several components (2 - 5) can be tested
VLE = vapor liquid equilibrium
Gas components
*
Condensable
K value data is required
Liquid phase data (see Table 2 in the STARS User's Guide)
CH4 in oil; CO2 in oil and water
Solution gas pseudo component
Distribution of light hydrocarbons
Component exists only in gas phase (N2, CO, O2, etc.)
Solubility is negligible
No liquid phase data
*
Oxidation reactions assume O2 in gas phase
Fuel-O2 mixing in kinetics
Products may be lumped, stoichiometry must be considered
COx, where 1 x 2
Trace of products requires separate components
Ratio of CO/CO2 depends on temperature
CO2 product can swell and mobilize oil
*
Solid occupies pore volume and has to be accounted for
Solid can be transported through phases (oleic or aqueous or both)
*
*
DENSITIES – Pure densities at reference conditions
Using linear or non-linear mixing rule to calculate phase (oleic or aqueous) density
The units of the densities will determine the unit of the conservation equation
STARS uses mole units because phase equilibrium and chemical reaction calculations are based on moles
Densities units in STARS are moles per unit volume
*
Gas phase
The mole density of the gas phase is calculated internally from g = p / RTZ
There are two ways to obtain Z
The ideal gas method assumes that Z = 1
The second method uses the Redlich-Kwong equation-of-state and typically predicts Z varying from 0.3 to 1.2
*
CMG Simulation Technology
A phase may be regarded as a physical manifestation of components
For example, the component water commonly may be found in the liquid, gaseous and solid phases
It is the phase that possesses tangible properties such as density and viscosity
All physical properties are assigned to a component in terms of the phases in which that component may be found
*
Viscosity
Again either using linear or non linear mixing rule to represent the viscosity changes due to components mixing
*
CMG Simulation Technology
There are three ways to input component phase viscosity in STARS
Use internal table with a possible dependence on salt concentration which can be significant (water only)
Use the correlation = a • exp (b/T), where ‘T’ is in absolute degrees
Enter directly a table of versus T
*
K-values input using correlations
Allows liquid-liquid K-values to represent components transferring from one (aqueous) phase to another (oleic) phase
*
CMG Simulation Technology
Liquid-liquid K-values can be compositional dependent (major feature to be used in chemical flood process)
With liquid-liquid compositional dependent K-values, partition of components from one phase to another under different operating condition can be simulated
Example: Surfactant partition from water to oil
*
Other properties include molecular weight, heat capacity, critical pressure, critical temperature, fluid enthalpies, solid density, fluid compressibilities
*
CMG Simulation Technology
WinProp can be used to generate STARS’s component properties using tuned EOS
All essential laboratory experiments and tests should be incorporated to “regress” the EOS
After tuning, export the EOS parameters for STARS usage
*
Allow user to create or destroy components in the process
e.g. Hydrocarbon + Oxygen CO2 + H2O
User can define the process to be exothermic (+energy) or endothermic (-energy)
User can define the speed of reaction (frequency factor)
*
Multi-reaction kinetics are allowed
*
CMG Simulation Technology
Solids created in the process can be transported through the phases (water or oil, NOT IN GAS)
If the solid particle size is greater than pore throat, blockage occurs
Blockage in STARS is indicated by reduction in Permeability using multiplier
*
Represented by Langmuir correlation and adsorption is a function of concentration and/or temperature
Each gridblock can have its own set of adsorption curve to represent different rock character
Again, if adsorption occurs, blockage will occur
Adsorption can also be fully or partial reversible
*
STARS also offers effective molecular diffusion, mechanical dispersivity, total dispersion in oil, water, or gas phase in I,J, K direction
These features are used to simulate the flow of tracers or chemicals due to concentration gradient (NOT pressure gradient)
*
Finite element strain grid collocated with finite difference flow grid
Visualization of strain
Used as chemical simulators
*
*
CMG Simulation Technology
A mathematical model accounting for the propagation of (true, pseudo, and/or dispersed phase) components through a porous medium and their effects on fluid and rock properties
Can be employed as a multi-component, multi-phase isothermal reservoir simulator
(Full material / mass balance equations)
*
CMG Simulation Technology
A mathematical model accounting for the propagation of heat through a porous medium and its effect on fluid and rock properties
(Full energy balance equation)
Stable implicit formulation
*
*
Water
Water is a standard component, and internal defaults are available for
Density, viscosity, enthalpy, heat capacity
Polymer solution
*
Internal water K values
Salt, ion component
*
Pure components
Chemicals of interest, soluble in oil (CO2, H2S, naptha, etc.)
Gas components, when soluble in oil (N2, O2, etc.)
*
e.g. methane, propane, hexane, oxygen, CO2, decane, etc.
*
Oil component in black-oil model
Pairs or limited groups (C7 - C9)
Entire ranges of molecular weight (Mw = 200 to 400)
Distribution of molecular species is fixed
*
Choice of oil components
For EOR processes, the choice of oil components is usually determined entirely by the type of mechanisms important to the EOR process to be modeled, for example:
Vaporization
A single component with zero K value (dead oil) allows for no vaporization or distillation
Single component with non zero K value allows for vaporization, but no distillation
Need at least two components for distillation (oil and solution gas in black-oil model)
*
Reactions are between oil components
Reaction models and strategy may determine what oil components to use
Cracking fuel from asphaltene
e.g. Hydrocarbon + Oxygen CO2 + H20 + Energy
*
CMG Simulation Technology
Temperature dependence of many properties can be estimated by running the EOS package at various temperatures (WinProp)
An oil can be characterized accurately from PVT and VLE lab data with many components (10 - 20), and then the result of lumping to several components (2 - 5) can be tested
VLE = vapor liquid equilibrium
Gas components
*
Condensable
K value data is required
Liquid phase data (see Table 2 in the STARS User's Guide)
CH4 in oil; CO2 in oil and water
Solution gas pseudo component
Distribution of light hydrocarbons
Component exists only in gas phase (N2, CO, O2, etc.)
Solubility is negligible
No liquid phase data
*
Oxidation reactions assume O2 in gas phase
Fuel-O2 mixing in kinetics
Products may be lumped, stoichiometry must be considered
COx, where 1 x 2
Trace of products requires separate components
Ratio of CO/CO2 depends on temperature
CO2 product can swell and mobilize oil
*
Solid occupies pore volume and has to be accounted for
Solid can be transported through phases (oleic or aqueous or both)
*
*
DENSITIES – Pure densities at reference conditions
Using linear or non-linear mixing rule to calculate phase (oleic or aqueous) density
The units of the densities will determine the unit of the conservation equation
STARS uses mole units because phase equilibrium and chemical reaction calculations are based on moles
Densities units in STARS are moles per unit volume
*
Gas phase
The mole density of the gas phase is calculated internally from g = p / RTZ
There are two ways to obtain Z
The ideal gas method assumes that Z = 1
The second method uses the Redlich-Kwong equation-of-state and typically predicts Z varying from 0.3 to 1.2
*
CMG Simulation Technology
A phase may be regarded as a physical manifestation of components
For example, the component water commonly may be found in the liquid, gaseous and solid phases
It is the phase that possesses tangible properties such as density and viscosity
All physical properties are assigned to a component in terms of the phases in which that component may be found
*
Viscosity
Again either using linear or non linear mixing rule to represent the viscosity changes due to components mixing
*
CMG Simulation Technology
There are three ways to input component phase viscosity in STARS
Use internal table with a possible dependence on salt concentration which can be significant (water only)
Use the correlation = a • exp (b/T), where ‘T’ is in absolute degrees
Enter directly a table of versus T
*
K-values input using correlations
Allows liquid-liquid K-values to represent components transferring from one (aqueous) phase to another (oleic) phase
*
CMG Simulation Technology
Liquid-liquid K-values can be compositional dependent (major feature to be used in chemical flood process)
With liquid-liquid compositional dependent K-values, partition of components from one phase to another under different operating condition can be simulated
Example: Surfactant partition from water to oil
*
Other properties include molecular weight, heat capacity, critical pressure, critical temperature, fluid enthalpies, solid density, fluid compressibilities
*
CMG Simulation Technology
WinProp can be used to generate STARS’s component properties using tuned EOS
All essential laboratory experiments and tests should be incorporated to “regress” the EOS
After tuning, export the EOS parameters for STARS usage
*
Allow user to create or destroy components in the process
e.g. Hydrocarbon + Oxygen CO2 + H2O
User can define the process to be exothermic (+energy) or endothermic (-energy)
User can define the speed of reaction (frequency factor)
*
Multi-reaction kinetics are allowed
*
CMG Simulation Technology
Solids created in the process can be transported through the phases (water or oil, NOT IN GAS)
If the solid particle size is greater than pore throat, blockage occurs
Blockage in STARS is indicated by reduction in Permeability using multiplier
*
Represented by Langmuir correlation and adsorption is a function of concentration and/or temperature
Each gridblock can have its own set of adsorption curve to represent different rock character
Again, if adsorption occurs, blockage will occur
Adsorption can also be fully or partial reversible
*
STARS also offers effective molecular diffusion, mechanical dispersivity, total dispersion in oil, water, or gas phase in I,J, K direction
These features are used to simulate the flow of tracers or chemicals due to concentration gradient (NOT pressure gradient)
*
Finite element strain grid collocated with finite difference flow grid
Visualization of strain